set term eps
set output "optimization_demon.eps"
set xrange [-1:1]
set samples 20
set arrow from -1+2.0/19*5, 1.2 to -1+2.0/19*5, 0.8
set label "approximation" at -1+2.0/19*5, 1.4 font "Arial,20"
set xlabel "x" font "Arial,20"
set ylabel "y" font "Arial,20"
plot x*x+x+1 with line lw 3 title "f(x)=x^2+x+1", x*x+x+1 with i title "discrete points"
